Doctors for paper making machines

ABSTRACT

A doctor for doctoring a roll of a paper making or other machine comprising a support for a doctor blade, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle, which extends substantially for the whole length of the doctor blade, communicates with the suction duct and is effective to transfer to the suction duct dust or dirt removed from the roll by the doctor blade, one wall of the suction nozzle being constituted by the doctor blade and its support and the other and facing wall of the suction nozzle extending substantially to the tip of the doctor blade.

United States Patent [1 1 Boyland [451 Aug. 20, 1974 [5 DOCTORS FOR PAPER MAKING MACHINES [75] Inventor: Albert Henry John Boyland,

' London, England [73] Assignee: Vickerys Limited, London, England [22] Filed: May 3, 1973 [21-] Appl. No: 356,806

[30] Foreign Application Priority Data May 4, 1972 Great Britain 20786/72 June 30, 1972 Great-Britain 30805/72 Dec. 6, 1972 Great Britain 56285/72 [52] US. Cl 15/301, 15/256.51, 15/308,

51] Int. Cl. B311 1/14, D2lg 3/00 [58] Field of Search 15/25651, 308, 301, 415

[56] References Cited UNITED STATES PATENTS 3,526,017 9/1970 Kleimola 15/308 3,687,730 8/1972 Murphy et al. 15/308 Primary Examiner--Leon G. Machlin Attorney, Agent, or FirmWatson, Cole, Grindle 8L Watson [57] ABSTRACT A doctor for doctoring a roll of a paper making or other machine comprising a support for a doctor blade,a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle, which extends substantially for the whole length of the doctor blade, communicates with the suction duct and is effective to transfer to the suction duct dust or dirt removed from the roll by the doctor blade, one wall of the suction nozzle being constituted by the doctor blade and its support and the other and facing wall of the suction nozzle extending substantially to the tip of the doctor blade.

13 Claims, 8 Drawing Figures PATENTEDmczo m4 SHEET '4 OF 6 PATENTEmuszo new SHEET 8 BF 6 1 a DOCTORS FOR PAPER MAKING MACHINES This invention relates to a doctor for doctoring a roll of a paper making or other machine of the type comprising a support for a doctor blade, a suction duct extending for substantially the whole length of the doctor blade and a suction nozzle communicating with the suction duct and serving to transfer to the suction duct dust and dirt removed from the roll by the doctor blade.

In U.S. Pat. No. 3,264,673 I have described a doctor of this type in which the nozzle is constituted by contiguous suction slots and provides a continuous wall extending rearwardly at a gradual inclination to the side of the doctor blade remote from the roll and in which each suction slot contains a readily removable orifice plate accommodatedin a slot therein, the orifice plates having graded circular holes which provide uniformity of suction through the suction slots.

blade and experience has shown that the suction effect at the critical zone, namely the zone of contact between the tip of the doctor blade and the roll, is very inefficient because the air is drawn into the nozzle by the suction mainly from above the wall and around its narrow forward zone and therefore fails to entrain the dirt on or adjacent to the tip of the blade. It has also transpired that, when the doctor is installed in the drying section of a paper making machine, parts of the machine tend to mask the suction slots containing the orifice plates having the smaller holes with the result that these suction'slots tend to be starved of suction and that, in practice, little if any graduation in effective area of the nozzle sections is required to obtain substantial uniformity of suction over the length of the blade.

With a view to overcoming these disadvantages, the invention provides a doctor for doctoring a roll of a paper making or other machine comprising a support for a doctor blade, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle, which extends substantially for the whole length of the doctor blade, communicates with the suction duct and is effective to transfer to the suction duct dust or dirt removed from the roll by the doctor. blade, one wall of the suction nozzle being constituted by the doctor blade and its support and the other and facing wall of the suction nozzle extending substantially to the tip of the doctor blade.

The forward end of the facing wall of the suction nozzle is preferably turned outwardly away from the doctor blade. In a preferred embodiment of the invention the facing wall of the suction nozzle is a hood extending forwardly from the suction duct and having a bulbous nose at its forward end.

Since the facing wall of the suction nozzle extends to the tip of the blade the suction effect is concentrated at the tip of the blade. When the facing wall of the suction nozzle is turned away from the blade, and particularly when it terminates in a bulbous nose, it largely prevents air from being drawn over the surface of the facing wall remote from the blade in a current bypassing the tip of the blade.

A bulbous nose on the facing wall provides an aerodynamic profile which minimizes turbulence in the air stream flowing around the hood into the suction nozzle. It is important to avoid such turbulence so far as possible because it interferes with the airflow over the tip of the blade and therefore detracts from the efficient removal of dust and-fluff from the blade tip. Curvature of the nose in the manner described later has been found effective in ensuring that the air flowing around the nose into the suction nozzle will follow the contour of the nose.

The facing wall, whether bulbous or not, should not project more than inch beyond the blade tip, otherwise there would be a tendency for it to foul the roll as the blade wears. The facing wall should not terminate short of the blade tip by more than k inch to ensure effective application of suction to the blade tip.

The depth of the suction nozzle is not critical, save to the extent that if it is too small there is a risk of blockage by broke (i.e. a mass of paper arising from breakage of the web of paper in the paper making machine) and of fouling (i.e. the nozzle contacting) the roll when the blade wears, whereas if it is too large the velocity of the entering air is so reduced as to preclude effective dust removal. A depth of /8 inch is preferred.

Preferably the hood is made up of contiguous unit sections which can be fitted together in the number required to accommodate the doctor to rolls of different lengths, the sections having forwardly extending webs which separate the suction nozzle into a series of adjacent suction slots. 1

Preferably also an air blast gallery is provided in the nose of the hood through which an air blast can be directed intermittently in a rearward direction into the suction nozzle to remove accumulations of dust.

The hood may be pivoted to the suction duct and urged into sealing engagement with the blade holder by a pneumatic piston and cylinder assembly.

In the event of breakage of the paper web, broke could accumulate in the suction nozzle, so tending to lift the hood and ultimately overcome the bias on the suction doctor and lift the blade off the roll, with the result that the broke would wrap around the roll.

With a view to preventing this the present invention provides an air gallery, communicating with at least one port which is normally closed by the hood but will be opened in response to lifting of the hood, means for supplying to the gallery air at a pressure different from atmospheric pressure, a pressure sensitive switch which operates in response to change of pressure in the gallery arising from lifting of the hood, and means responsive to operation of said switch for reversing the pressure and exhaust connections to the piston and cylinder assembly and thereby lifting the hood to a raised position.'Any tendency of the bias on the suction doctorto be overcome is thus avoided. v

Preferably the gallery communicates with a series of ports spaced apart in a member supporting the blade holder in the longitudinal direction of the hood and contains pressurized air, the outlets of the ports being normally sealed by the hood.

Certain embodiments of doctor according to the invention will now be described, by way of example, with reference to the accompanying drawings,in which:

FIG. 1 is a front elevation of part of a doctor according to the invention,

FIG. 2 is a corresponding plan view,

FIG. 3 is a corresponding cross section,

FIG. 4 is a pneumatic circuit diagram,

FIG. 5 is an electrical circuit diagram,

FIG. 6 illustrates an alternative form of doctor, FIG. 7 illustrates a third embodiment, and

FIG. 8 is a section on the line VIIIVIII in FIG. 7.

In the construction shown in FIGS. 1-3, a suction duct 10, to one end of which suction is applied in use of the doctor, carries a forwardly extending wall 11 on which is supported a blade holder 12 carrying a doctor blade 13 and a pressure plate 14. The duct is supported in conventional manner so that the tip of the blade 13 is biassed into contact with a roll 15 to be doc tored.

Mounted on the duct 10 is a hood consisting of individual sections 16 disposed end to end and attached by grub screws to a tube 17, journalled in brackets 18 fixed to the duct 10. Arms 19 attached to opposite ends of the tube 17 are pivoted to the piston rods 20 of double acting air cylinders 21, of which one only is shown in FIGS. 1-3. Both are shown in the pneumatic circuit diagram in FIG. 4.

Each section 16 of the hood has spaced forwardly extending webs 22 which are normally urged by the cylinders 21 into sealing engagement with the members 11, 12 and the outer surface of the duct 10. The hood may be moulded from rubber or of cast light metal alloy carrying rubber strips 39 to form a seal against the members ll, 12 and 10. As best shown in FIG. 1, the webs 22 define between them a series of suction slots 23 which communicate with corresponding slots 24 (FIG. 3) in the duct 10. The mouths of the slots 23 are of the same width as the slots 24 and, as will be seen from FIG. 2, each suction slot 23 is of substantially constant cross sectional area throughout and affords no obstruction to the flow of air or material sucked from the doctor blade.

Each of the hood sections 16 is continued forwardly of the webs 22 to form a bulbous nose 25 which terminates level with the tip of the blade 13 when new. It will be noted that the nose 25 has a convex curvature 36 where its front end merges into the surface facing the blade 13 and a concave curvature 37 when it merges into the face of the hood l6 remote from the blade 13 to minimise turbulence in the air flowing around the nose into the suction slot. The noses 25 of adjoining sections abut end to end and define with the blade 13 an uninterrupted suction nozzle 26, through which air is drawn into the suction slots 23, of depth sufficient to ensure that when the blade has worn down the hood will not foul the roll. The noses 25 are hollow and provide an air gallery 27, into one end of which a blast of air may be blown intermittently. One end of the gallery is closed by a rubber end plug 28 and adjoining sections of the gallery are joined by tubular rubber plugs 29. The air blown into the gallery 27 is discharged rearwardly through ducts 30 towards the suction slots 23.

Should it be desired to provide a gradation in effective areas of the suction slots 23 this can be achieved by filing away ledges 31 at the rear of the slots. Alternatively flexible strips may be fitted in the vicinity of the ledges 31 and adjusted by external adjusting screws to provide local variation of the cross sectional area of the rear ends of the nozzles.

The air pressure in the cylinders 21 applies torque to the hood to hold it in sealing engagement with the duct l0 and the members 11 and 12. This pressure may be suitably adjusted in accordance with whether the blade 13 is bearing against the upper or the lower side of a roll and gravity is therefore assisting or counteracting the sealing action. The cylinders 21 are operative to raise the hood to the position shown in chain-dotted lines in FIG. 3 to facilitate cleaning or removal of broke from the hood.

Due to the fact that the nose 25 overlaps the tip of the blade 13 any particles scraped from the roll and projected into the channel 26 are immediately entrained by the air stream induced by the suction. Any tendency of wet material scraped from the roll to dry on and remain on the blade is therefore minimised.

As shown in FIG. 3, a gallery 34 communicates with a series of ports 35 in the wall 11 which are spaced apart in the longitudinal direction of the hood and are sealed by the webs 22 of the hood when the latter is in its normal down position.

In operation of the doctor and as shown in FIG. 4 air under pressure is admitted through a filter 40, a nonreturn valve 41, a pressure regulator 42 and a restrictor 43 to the gallery 34.

The air under pressure also normally passes through a five port valve 46 and a pressure regulator 47 to the pneumatic loading cylinders 21 in the direction to maintain the hood in its lowered position in which it seals the ports 35.

If the nose 25 tends to lift under the action of the pressure of broke, one or more of the 35 will be unsealed. A pressure switch 49, sensitive to the air pressure in the gallery 34, then moves to its alternative position to energize a solenoid 50. After removing the broke the hood may be returned to position, admitting air under pressure to the opposite ends of the cylinders 21 through a pressure regulator 51 and lifting the hood to the fully raised position. After removing the broken portion the hood may be returned to the down position by depressing a push button 52 (FIG. 5) to de-energize the solenoid 50. A spring 53 (FIG. 4) then returns the valve 46 to its original position. The push button 52 is held depressed until a lamp 54 (FIG. 5) lights to show that the valve 46 has changed over. Another lamp 55 is lit when the solenoid 50 is energized to show that the hood is raised.

Another push button 56 can be utilized to energize the solenoid 50 to raise the hood when it is desired to clean it.

Restrictors 57 connected to the exhaust outlets of the valve 46 serve to regulate the speed of operation of the cylinders 21.

In the embodiment shown in FIG. 6, the hood 116 is a plate, the forward end of which is turned outwardly away from the doctor blade 13 to form a flange 117.

In the embodiment shown in FIGS. 7 and 8, valve stems 60, urged upwardly by springs 61, are provided in apertures in the wall 11 beneath the webs 22. When the hood 16 is down, the valve stems 60 are depressed to force sealing discs 63 to seal leakage holes 64 in an air pressure pipe 65 which corresponds to the gallery 34 shown in FIGS. 1 and 4. Slight upward movement of the hood 16 under the pressure of broke will cause one or more of the sealing discs 63 to lift, under the pressure of one or more of the springs 61, to allow air to leak through a hole 64 from the pipe 65, thereby causing the cylinders 21 to lift the hood 16 to the position shown in chain-dotted lines as already described with reference to FIG. 4.

What I claim as my invention and desire to secure by Letters Patent is:

1. A doctor for doctoring a roll of a paper making or other machine comprising a support for a doctor blade, a doctor blade mounted on said support, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle, which extends substantially for the whole length of the doctor blade, communicates with the suction duct at its rear end by a substantially uninterrupted slot extending parallel to the doctorblade and has at its forward end a slot-like mouth substantially devoid of interruptions, the whole length of said mouth being free to accept dirt by suction in operation at the doctor for transfer to the suction duct of dust or dirt removed from the roll by the doctor blade, said suction nozzle, throughout its width, providing at all times free and substantially unimpeded passage for dirt from the doctor blade to the suction duct and one wall of the suction nozzle being constituted by the doctor blade and its support and the other end facing wall of the nozzle extending substantially to the tip of the doctor blade and having a forward end which is turned outwardly away from the doctor blade.

2. A doctor as claimed in claim 1, in which the facing wall of the suction nozzle is a hood extending forwardly from the suction duct and having a bulbous nose at its forward end.

3. Adoctor as claimed in claim 2, in which the bulbous nose has a convex curvature where its front end merges into the surface facing the doctor blade and a concave curvature where it merges into the surface of the hood remote from the blade.

4. A doctor as claimed in claim 2, in which the hood has forwardly extending webs which sub-divide the suction nozzle into a series of adjacent slots.

5. A doctor as claimed in claim 2, in which the hood is made up of contiguous mating sections.

6. A doctor as claimed in claim 2, in which the bulbous nose contains an air blast gallery through which air can be directed intermittently in a rearward direction into the suction nozzle to remove accumulations of dirt.

7. A doctor for doctoring the roll of a paper making machine comprising a support, a doctor blade mounted on said support, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle which extends substantially for the whole length of the doctor blade, communicates with the suction duct and is effective to transfer to the suction duct dust and dirt removed from the roll by the doctor blade, one wall of the suction nozzle being constituted by the doctor blade and its support and the other end facing wall of the suction nozzle being constituted by a hood extending forwardly from the suction duct substantially to the tip of the doctor blade and said hood being pivoted to the suction duct and urged into sealing engagement with the blade holder by a piston and cylinder assembly.

8. A doctor as claimed in claim 7, which includes an air gallery, communicating with at least one port which is normally closed by the hood but will be opened in response to lifting of the hood, means for supplying to the gallery air at a pressure different from atmospheric pressure, a pressure sensitive switch which operates in response to change of pressure in the gallery arising from lifting of the hood, and means responsive to operation of said switch for reversing the pressure and exhaust connections to the piston and cylinder assembly and thereby lifting the hood to a raised position.

9. A doctor as claimed in claim 8, in which the air gallery communicates with a series of ports spaced apart in the longitudinal directionof the hood and contains pressurized air, the outlets of the ports being normally sealed by the hood.

10. A doctor as claimed in claim 8, in which the air gallery has a plurality of leakage holes and which includes a series of pins interposed between sealing members and the hood and springs urging the sealing members upwardly, the sealing members being held down by the pins when the hood is pressed against the blade holder by the piston and cylinder assembly but being capable of lifting to allow air to escape from the gallery if the hood should be lifted slightly by the pressure of broke.

11. A doctor as claimed in claim 1, in which the facing wall is a plate having at its forward end a flange turned outwardly away from the doctor blade.

12. A doctor as claimed in claim 7, wherein the hood has a bulbous nose at its forward end.

13. A doctor as claimed in claim 7, wherein the hood has at its forward end a flange turned outwardly away from the doctor blade. 

1. A doctor for doctoring a roll of a paper making or other machine comprising a support for a doctor blade, a doctor blade mounted on said support, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle, which extends substantially for the whole length of the doctor blade, communicates with the suction duct at its rear end by a substantially uninterrupted slot extending parallel to the doctor blade and has at its forward end a slot-like mouth substantially devoid of interruptions, the whole length of said mouth being free to accept dirt by suction in operation at the doctor for transfer to the suction duct of dust or dirt removed from the roll by the doctor blade, said suction nozzle, throughout its width, providing at all times free and substantially unimpeded passage for dirt from the doctor blade to the suction duct and one wall of the suction nozzle being constituted by the doctor blade and its support and the other end facing wall of the nozzle extending substantially to the tip of the doctor blade and having a forward end which is turned outwardly away from the doctor blaDe.
 2. A doctor as claimed in claim 1, in which the facing wall of the suction nozzle is a hood extending forwardly from the suction duct and having a bulbous nose at its forward end.
 3. A doctor as claimed in claim 2, in which the bulbous nose has a convex curvature where its front end merges into the surface facing the doctor blade and a concave curvature where it merges into the surface of the hood remote from the blade.
 4. A doctor as claimed in claim 2, in which the hood has forwardly extending webs which sub-divide the suction nozzle into a series of adjacent slots.
 5. A doctor as claimed in claim 2, in which the hood is made up of contiguous mating sections.
 6. A doctor as claimed in claim 2, in which the bulbous nose contains an air blast gallery through which air can be directed intermittently in a rearward direction into the suction nozzle to remove accumulations of dirt.
 7. A doctor for doctoring the roll of a paper making machine comprising a support, a doctor blade mounted on said support, a suction duct extending for substantially the whole length of the doctor blade, and an elongated slot-like suction nozzle which extends substantially for the whole length of the doctor blade, communicates with the suction duct and is effective to transfer to the suction duct dust and dirt removed from the roll by the doctor blade, one wall of the suction nozzle being constituted by the doctor blade and its support and the other end facing wall of the suction nozzle being constituted by a hood extending forwardly from the suction duct substantially to the tip of the doctor blade and said hood being pivoted to the suction duct and urged into sealing engagement with the blade holder by a piston and cylinder assembly.
 8. A doctor as claimed in claim 7, which includes an air gallery, communicating with at least one port which is normally closed by the hood but will be opened in response to lifting of the hood, means for supplying to the gallery air at a pressure different from atmospheric pressure, a pressure sensitive switch which operates in response to change of pressure in the gallery arising from lifting of the hood, and means responsive to operation of said switch for reversing the pressure and exhaust connections to the piston and cylinder assembly and thereby lifting the hood to a raised position.
 9. A doctor as claimed in claim 8, in which the air gallery communicates with a series of ports spaced apart in the longitudinal direction of the hood and contains pressurized air, the outlets of the ports being normally sealed by the hood.
 10. A doctor as claimed in claim 8, in which the air gallery has a plurality of leakage holes and which includes a series of pins interposed between sealing members and the hood and springs urging the sealing members upwardly, the sealing members being held down by the pins when the hood is pressed against the blade holder by the piston and cylinder assembly but being capable of lifting to allow air to escape from the gallery if the hood should be lifted slightly by the pressure of broke.
 11. A doctor as claimed in claim 1, in which the facing wall is a plate having at its forward end a flange turned outwardly away from the doctor blade.
 12. A doctor as claimed in claim 7, wherein the hood has a bulbous nose at its forward end.
 13. A doctor as claimed in claim 7, wherein the hood has at its forward end a flange turned outwardly away from the doctor blade. 